Optical interference coating and lamps using same

Abstract

Optical interference coatings useful on lamps for transmitting visible light radiation at about 90% average from 400-770 nm and for reflecting infrared radiation comprise three spectrally adjacent multiperiod stacks of alternating high and low index of refraction layers. Compared to conventional filters, these filters have a greater tolerance to layer thickness variations incurred during manufacture with little or no color shift when viewed at non-normal angles.

What is claimed is: 
     
       1. An optical interference coating for reflecting infrared radiation and transmitting visible light radiation which comprises three spectrally adjacent, multiperiod stacks wherein each stack has at least two periods with one of the stacks being a short wave pass stack and with said second and third stacks spectrally located at wavelengths longer than that of said first stack and different from each other, said periods of said second and third stacks containing seven alternating layers of high and low refractive index materials of the form: ##EQU4## wherein ≦ a≦4 5≦b≦15   5≦c≦15   1≦d≦2.5 and wherein L and H are the low and high index of refraction materials, respectively, L and H each being defined as having an optical thickness of a quarterwave of the stack wavelength.     
     
     
       2. The coating of claim 1 wherein said layers H/b and L/c have an optical thickness no greater than one-twentieth of the stack wavelength. 
     
     
       3. The coating of claim 2 wherein said short wave pass stack is a quarterwave stack. 
     
     
       4. The coating of claim 3 wherein said quarterwave stock contains periods of the form: ##EQU5## 
     
     
       5. The coating of claim 4 wherein said first and seventh layers in said second and third stacks have an optical thickness less than that of said low refractive index layers in said periods of said short wave pass stack. 
     
     
       6. The coating of claim 4 wherein said central layer of said periods in said second and third stacks has an optical thickness less than that of said high refractive index layer in said periods of said short wave pass stack. 
     
     
       7. The coating of claim 6 refined by computer optimization. 
     
     
       8. The coating of claim 6 wherein said layers comprise refractory metal oxide. 
     
     
       9. The coating of claim 1 refined by computer optimization. 
     
     
       10. The coating of claim 9 wherein said layers comprise refractory metal oxide. 
     
     
       11. The coating of claim 1 wherein said layers comprise refractory metal oxide. 
     
     
       12. An electric lamp comprising a light transmissive envelope containing an electric light source within wherein at least portion of said envelope is coated with an optical interference coating for reflecting infrared radiation and transmitting visible light radiation said coating having a spectrally broad high transmittance of at least 90% average between about 400 to 770 nm and a spectrally broad high reflectance of at least about 70% average between about 800 to 2900 nm and comprising three spectrally adjacent, multiperiod stacks wherein each stack has at least two periods with one of said stacks being a short wave pass stack and with said second and third stacks spectrally located at wavelengths longer that that of said first stack and different from each other, said periods of said second and third stacks each containing seven alternating layers of high and low refractive index materials of the form: ##EQU6## wherein ≦ a≦4 5≦b≦15   5≦c≦15   1≦d≦2.5, wherein L and H are the low and high index of refraction materials, respectively, L and H each being defined as having an optical thickness of a quarterwave of the stack wavelength, and wherein the layers H/b and L/c have an optical thickness less than one-twentieth of the stack wavelength.     
     
     
       13. The lamp of claim 12 wherein said short wave pass stack of said coating is a quarterwave stack. 
     
     
       14. The lamp of claim 13 wherein said quarterwave stack contains periods of the form: ##EQU7## 
     
     
       15. The lamp of claim 37 wherein said first nd seventh layers in said second and third stacks of said coating have an optical thickness less than that of said lower refractive index layers in said periods of said short wave pass stack. 
     
     
       16. The lamp of claim 15 wherein said central layer of said periods in said second and said third stacks has an optical thickness less than that of said high refractive index layer in said short wave pass stack. 
     
     
       17. The lamp of claim 16 wherein said layers comprise refractory metal oxide. 
     
     
       18. The lamp of claim 12 wherein said layers comprise refractory metal oxide. 
     
     
       19. The lamp of claim 18 wherein said light transmissive envelope consists essentially of fused silica. 
     
     
       20. The lamp of claim 18 wherein said light transmissive envelope is a high temperature glass. 
     
     
       21. The lamp of claim 12 wherein said light transmissive envelope comprises fused silica. 
     
     
       22. The lamp of claim 12 wherein said light transmissive envelope comprises glass. 
     
     
       23. A tungsten halogen incandescent lamp comprising a vitreous, light transmissive envelope having a filament chamber with a tungsten filament and at least one halogen hermetically enclosed within said chamber, wherein said filament has a longitudinal axis which is radially aligned along the optical center of said chamber with at least a portion of the outer surface of said chamber coated with an optical interference coating for reflecting infrared radiation and transmitting visible light radiation, said coating comprising three spectrally adjacent, multiperiod stacks wherein each stack has at least two periods with one of said stacks being a shortwave pass stack and with said second and third stacks spectrally located at wavelengths longer than that of said first stack and different from each other, said periods of said second and third stacks each containing seven alternating layers of high and low refractive index materials of the form: ##EQU8## wherein ≦ a≦4 5≦b≦15   5≦c≦15   1≦d≦2.5 and wherein L and H represent the low and high index of refraction materials, respectively, L and H each being defined as having an optical thickness of a quarterwave of the stack wavelength.     
     
     
       24. The lamp of claim 23 wherein said shortwave pass stack is a quarterwave stack containing periods of the form: ##EQU9## 
     
     
       25. The lamp of claim 24 wherein said first and seventh layers in said second and third stacks of said coating have an optical thickness less than that of said low refractive index layers in said periods of said shortwave pass stack. 
     
     
       26. The clamp of claim 25 wherein said central layer of said periods in said second and said third stacks has an optical thickness less than that of said high refractive index layer in said shortwave pass stack. 
     
     
       27. The lamp of claim 26 wherein said layers comprise refractory metal oxide. 
     
     
       28. The lamp of claim 27 wherein said light transmissive envelope comprises fused silica. 
     
     
       29. The lamp of claim 28 wherein said coating has a spectrally broad transmittance of at least about 90% average between 400 to 770 nm and a spectrally broad high transmittance of at least about 70% average between about 800 to 1900 nm.